As illustrated in FIG. 1, the conventional way of making a mortise is to use a machining tool provided with a cutter 1 by means of which a mortise 3 is made in a piece of wood 2. The mortise 3 is shaped and dimensioned to receive a tenon 4. The conventional mortise making device is made as an integral part of the structure of a machining tool and is therefore not detachable. As a result, the machining tool can not be used for other finishing works.